Devices for infusing to a patient a beneficial agent such as a drug diffused in a medical liquid are known in the art. The most common device utilizes an elevated glass or flexible container having the beneficial agent diffused in a medical liquid which is fed by gravity to a patient's venous system via a length of flexible plastic tubing and a catheter. The rate of flow in this setup is commonly regulated by an adjustable clamp on the tubing. This setup suffers from the drawback of requiring a relatively stationary patient and is dependent on the height differential between this source of liquid and the patient for accurate delivery rates.
An additional type of infusion device utilizes electro-mechanical components in a pump to provide fluid propulsion of the liquid for infusion into the patient. Such electronically controlled infusion devices, however, suffer from several drawbacks including the cost of such electrical components as well as the limit such electrical components and the necessary power source place on the size and thus portability of the device.
Devices in the art are also utilized which employ an elastomeric bladder which contains the liquid to be infused under pressure for infusion. Such elastomeric bladder infusion devices are seen in U.S. Pat. No. 4,741,733 to Winchell et al. and U.S. Pat. No. 4,769,008 to Hessel, both of which are assigned to the assignee of the present invention.
While such elastomeric bladder infusion devices such as seen in the Hessel and Winchell et al. patents provide an accurate flow of the liquid being infused over an extended period of time, the rate of flow of the liquid being infused is limited to a single flow rate. While electro-mechanical pumping devices can include circuitry to allow programming of a variety of sequential flow rates, such additional electrical components further add to the size and cost of such devices. In the gravity fed type of infusion device, sequential infusion rates are achieved by manually adjusting the adjustable flow clamp.
What would thus be desirable would be an infusion device capable of providing sequential flow rates of the infused liquid which would be portable to allow the patient free movement while providing for sequential flow rates. Additionally, such device should not be cost prohibitive. The present invention meets these requirements.